Mental Fatigue Impairs Endurance Performance: A Physiological Explanation

Fatigued or bored? Investigating the effect of different types of mental fatigue on 3 km running performance

Mental fatigue has been highly cited as having a negative impact on endurance performance. Few, however, have investigated whether different types of mental fatigue, namely active and passive fatigue, might affect endurance performance differently. This study used a repeated-measures design where 11 participants completed a 3 km run after three 32-min conditions: an actively fatiguing task (Task-load Dual-back; TloadDback); a passively fatiguing task (Mackworth Clock); and a control task (Documentary). Subjective ratings and performance on a second task (Flanker task) were taken before and after the 32-min tasks, while ratings of perceived effort, motivation and workload were taken during the 3 km run. Results showed that both fatigue conditions were mentally fatiguing, with the TloadDback rated as more demanding and the Mackworth Clock more boring and less motivating. Performance on subsequent tasks showed different effects: the TloadDback condition had the slowest responses on the post-test Flanker task, while the Mackworth Clock condition had the slowest completion time on the 3 km run, though this difference in completion times was non-significant. These results suggest that different cognitive tasks lead to different types of mental fatigue, which can lead to different outcomes on subsequent cognitive tasks but non-significant differences on subsequent physical tasks. This study highlights that to understand the influence of mental fatigue on physical performance, it is important to understand the cognitive tasks used and how different cognitive and physical tasks interact. Future work should examine whether performance outcomes in other areas commonly affected by mental fatigue, like technical and tactical sporting skills, are affected differently by active and passive fatigue.

Contextualising flexible nonlinear periodization as a person-adaptive behavioral model for exercise maintenance

There is a growing focus on developing person-adaptive strategies to support sustained exercise behaviour, necessitating conceptual models to guide future research and applications. This paper introduces Flexible nonlinear periodisation (FNLP) - a proposed, but underdeveloped person-adaptive model originating in sport-specific conditioning - that, pending empirical refinement and evaluation, may be applied in health promotion and disease prevention settings. To initiate such efforts, the procedures of FNLP (i.e., acutely and dynamically matching exercise demand to individual assessments of mental and physical readiness) are integrated with contemporary health behaviour evidence and theory to propose a modified FNLP model and to show hypothesised pathways by which FNLP may support exercise adherence (e.g., flexible goal setting, management of affective responses, and provision of autonomy/variety-support). Considerations for future research are also provided to guide iterative, evidence-based efforts for further development, acceptability, implementation, and evaluation.

Absence of Monotony and Strain Effects on Referees' Physical Performance During International Basketball Federation World Cup Basketball Competition

PURPOSE

The study aimed to conduct a comparative analysis of physical performance indicators and assess the levels of performance monotony and strain experienced by basketball referees.

METHODS

The study involved the participation of 12 basketball referees (mean age: 40.0 [4.9] y) affiliated with the International Basketball Federation. The investigation was carried out throughout 2 density tournaments, wherein the maximum heart rate, average heart rate, performance monotony, and performance strain were documented for 3 variables.

RESULTS

The findings indicated significant variations in the mean heart rate, maximum heart rate, total distance monotony, total distance strain, the total number of sprints monotony, the total number of sprints strain, calories monotony, and calories strain (P < .05). Decreasing the density of elite-level basketball competitions has been observed to reduce the monotony and strain experienced by referees. However, this action does not increase motion distance or speed zones.

CONCLUSIONS

The environmental stressors experienced by senior-level athletes (World Cup) differ from those encountered by younger athletes (World Cup Under 19). Further investigation is required to ascertain the potential effects of competition monotony and strain on decision-making processes and the overall quality of refereeing.

Creatine supplementation research fails to support the theoretical basis for an effect on cognition: Evidence from a systematic review

Creatine supplementation has been put forward as a possible aid to cognition, particularly for vegans, vegetarians, the elderly, sleep deprived and hypoxic individuals. However, previous narrative reviews have only provided limited support for these claims. This is despite the fact that research has shown that creatine supplementation can induce increased brain concentrations of creatine, albeit to a limited extent. We carried out a systematic review to examine the current state of affairs. The review supported claims that creatine supplementation can increases brain creatine content but also demonstrated somewhat equivocal results for effects on cognition. It does, however, provide evidence to suggest that more research is required with stressed populations, as supplementation does appear to significantly affect brain content. Issues with research design, especially supplementation regimens, need to be addressed. Future research must include measurements of creatine brain content.

Sleep deprivation increases the regularity of isometric torque fluctuations

The regularity of the fluctuations present in torque signals represent the adaptability of the motor control. While previous research showed how it is affected by neuromuscular fatigue and ageing, the underlying mechanisms remain unclear. It is currently under debate whether these changes are explained by central or peripheral neuromuscular mechanisms. Here, we experimentally manipulated the sleep of thirteen young adults through a supervised 24 h-sleep deprivation protocol. This study aimed to investigate the effect of sleep deprivation on the regularity of torque fluctuations, and other standard torque-related outcomes (Peak Torque - PT - and Rate of Torque Development - RTD). The participants were asked to perform knee extension maximal voluntary contractions (MVC) and submaximal knee extensions at 40% of MVC for 30 s. PT and RTD were calculated from the MVC and the regularity of the torque fluctuations was determined on the submaximal task through Sample Entropy (SampEn). In addition, rate of perceived effort (RPE) was collected. We found no significant changes in PT and RTD. The regularity of torque fluctuations significantly increased (i.e., a decrease in SampEn) after 24 h-sleep deprivation (PRE = 1.76 ± 0.268, POS24 = 1.71 ± 0.306; p = 0.044). Importantly, we found a negative correlation between RPE and SampEn relative changes after sleep deprivation. This study brings new insights towards the understanding of the underlying mechanisms that explain changes in torque fluctuations, demonstrating that these changes are not limited to neuromuscular processes but are also likely to be affected by other domains, such as psychological profile, which can indirectly affect the neural drive to the muscles.

Effect of mental fatigue on mean propulsive velocity, countermovement jump, and 100-m and 200-m dash performance in male college sprinters

The objective of this study was to analyze the effect of mental fatigue on mean propulsive velocity (MPV), countermovement jump (CMJ), 100, and 200-m dash performance in college sprinters. A total of 16 male athletes of sprint events (100 and 200-m dash) participated in this study. Each participant underwent two baseline visits and then running under the three experimental conditions. Assessments (MPV and CMJ) occurred both before and after either smartphone use (SMA) or Stroop task (ST), or watching a documentary TV show about the Olympic Games (CON). Then, the athletes ran the simulated race (i.e. the 100 and 200-m dash). There was no condition (p > 0.05) or time effect (p > 0.05) for MPV, CMJ, 100-m, or 200-m dash performance. In conclusion, the present study results revealed no mental fatigue effect induced by SMA or ST on neuromuscular, 100-m or 200-m dash performance in male college sprinters.

Transcranial Doppler Ultrasound and Concussion-Supplemental Symptoms with Physiology: A Systematic Review

Sport-related concussion (SRC) can impair the cerebrovasculature both acutely and chronically. Transcranial Doppler (TCD) ultrasound assessment has the potential to illuminate the mechanisms of impairment and provide an objective evaluation of SRC. The current systematic review investigated studies employing TCD ultrasound assessment of intracranial arteries across three broad categories of cerebrovascular regulation: neurovascular coupling (NVC), cerebrovascular reactivity (CVR), and dynamic cerebral autoregulation (dCA). The current review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42021275627). The search strategy was applied to PubMed, as this database indexes all biomedical journals. Original articles on TCD for athletes with medically diagnosed SRC were included. Title/abstract and full-text screening were completed by three authors. Two authors completed data extraction and risk of bias using the Methodological Index for Non-Randomized Studies and Scottish Intercollegiate Guideline Network checklists. Of the 141 articles identified, 14 met the eligibility criteria. One article used an NVC challenge, eight assessed CVR, and six investigated dCA. Methodologies varied widely among studies, and results were heterogeneous. There was evidence of cerebrovascular impairment in all three domains roughly 2 days post-SRC, but the magnitude and recovery of these impairments were not clear. There was evidence that clinical symptom resolution occurred before cerebrovascular function, indicating that physiological deficits may persist despite clinical recovery and return to play. Collectively, this emphasizes an opportunity for the use of TCD to illuminate the cerebrovascular deficits caused by SRC. It also highlights that there is need for consistent methodological rigor when employing TCD in a SRC population.

The Impact of Mental Fatigue on a Strength Endurance Task: Is There a Role for the Movement-Related Cortical Potential?

PURPOSE

Several mechanisms have been proposed to explain how mental fatigue degrades sport performance. In terms of endurance performance, a role for an increased perceived exertion has been demonstrated. Using electroencephalography and, more specifically, the movement-related cortical potential (MRCP), the present study explored the neural mechanisms that could underlie the mental fatigue-associated increase in perceived exertion.

METHODS

Fourteen participants (age, 23 ± 2 yr; 5 women, 9 men) performed one familiarization and two experimental trials in a randomized, blinded, crossover study design. Participants had to complete a submaximal leg extension task after a mentally fatiguing task (EXP; individualized 60-min Stroop task) or control task (CON; documentary). The leg extension task consisted of performing 100 extensions at 35% of 1 repetition maximum, during which multiple physiological (heart rate, electroencephalography) and subjective measures (self-reported feeling of mental fatigue, cognitive load, behand motivation, ratings of perceived exertion) were assessed.

RESULTS

Self-reported feeling of mental fatigue was higher in EXP (72 ± 18) compared with CON (37 ± 17; P < 0.001). A significant decrease in flanker accuracy was detected only in EXP (from 0.96 ± 0.03% to 0.03%; P < 0.05). No significant differences between conditions were found in MRCP characteristics and perceived exertion. Specifically in EXP, alpha wave power increased during the leg extension task ( P < 0.01).

CONCLUSIONS

Mental fatigue did not impact the perceived exertion or MRCP characteristics during the leg extension task. This could be related to low perceived exertion and/or the absence of a performance outcome during the leg extension task. The increase in alpha power during the leg extension task in EXP suggests that participants may engage a focused internal attention mechanism to maintain performance and mitigate feelings of fatigue.

Counteracting mental fatigue for athletes: a systematic review of the interventions

The deleterious effects of mental fatigue (MF) on athletes have been carefully studied in various sports, such as soccer, badminton, and swimming. Even though many researchers have sought ways to ameliorate the negative impact of MF, there is still a lack of studies that review the interventions used to counteract MF among athletes. This review aims to report the current evidence exploring the effects of interventions on MF and sport-specific performance, including sport-specific motor performance and perceptual-cognitive skills. Web of Science, Scopus, PubMed, and SPORTDicus (EBSCOhost) were combed through to find relevant publications. Additionally, the references and Google Scholar were searched for any grey literature. For the current review, we included only randomized controlled trials that involved athletes, a primary task to induce MF, interventions to counter MF with comparable protocols, and the outcomes of sport-specific motor performance and perceptual-cognitive skill. The selection criteria resulted in the inclusion of 10 articles. The manipulations of autonomous self-control exertion, person-fit, nature exposure, mindfulness, and transactional direct current stimulation showed that positive interventions counteract MF and improve sport-specific performance in different domains, including strength, speed, skill, stamina, and perceptual-cognitive skills. The selected interventions could significantly counteract MF and improve subsequent sport-specific performance. Moreover, self-regulation and attention resources showed the importance of the potential mechanisms behind the relevant interventions.

The influence of the perceived requirements of the next match and motivation on the mental fatigue of soccer players

The high cognitive and/or emotional demands of competition can lead to a state of mental fatigue which has shown to be detrimental to soccer performance. However, there is a need to further understand the true mental demands of soccer players. The aim of the present study was to analyze the influence of motivation and the perceived requirements of the next match on mental fatigue perceived by soccer players over the passing of a season. The combined effect of both variables on the perception of mental fatigue, as well as the influence of the time of the season on perceived mental fatigue, were also analyzed. Twenty-six semi-professional Spanish male players (M = 26.31 ± 5.18 years) participated in the present study, conducted during the 2020-2021 season. Perceived mental fatigue and motivation were measured at each training session. The perceived requirements of the next match were also measured in each of the competitive weeks. Linear mixed models were run with R Studio to examine the influence of motivation and the perceived difficulty of the next match on perceived mental fatigue, the combined effect of both variables on perceived mental fatigue, and the influence of the passing of the season on perceived mental fatigue. The results showed a negative and significant influence of motivation on perceived mental fatigue (p < 0.001) and a positive and significant influence of the perceived requirements of the next match on perceived mental fatigue (p < 0.001). Regarding the combined effect, there was a positive and significant effect (p < 0.01) of the perceived difficulty of the next match on the relation between motivation and perceived mental fatigue. A negative influence of season passage on perceived mental fatigue levels was found (p < 0.001). We recommended coaches to consider using the most motivating training tasks when higher next-match requirements are perceived and to be careful with avoidance strategies for mental fatigue, especially at the beginning of the season.

Relationship between Volitional and Non-Volitional Quadriceps Muscle Endurance in Patients with Chronic Obstructive Pulmonary Disease

Volitional assessment of quadriceps muscle endurance is clinically relevant in patients with chronic obstructive pulmonary disease (COPD). However, studies that determine the construct validity of volitional tests by comparing them to non-volitional measures are lacking. Therefore, the aim of the current study is to evaluate the correlation between volitional and non-volitional quadriceps muscle endurance in patients with COPD. Quadriceps muscle endurance was evaluated in twenty-six patients with COPD. A volitional isometric and a volitional isokinetic protocol were performed on a computerised dynamometer to determine the isometric time and isokinetic work fatigue index, respectively. Non-volitional assessment of quadriceps muscle endurance was evaluated using repetitive electrical stimulations to establish the isometric muscle force decline. Sixteen patients (61 ± 8 years, 63% male, FEV1 47 (32-53)%) performed all three quadriceps endurance tests conforming to pre-defined test criteria. Both volitional isometric time and isokinetic work fatigue index did not significantly correlate with non-volitional muscle force decline (both p > 0.05). There was a strong correlation between volitional isometric time and isokinetic work fatigue index (rho = -0.716, p = 0.002). To conclude, this study suggests that volitional measures evaluate partly different aspects of quadriceps muscle endurance compared to non-volitional measures. Accordingly, these outcome measures cannot be used interchangeably.

Effects of smartphone use before resistance exercise on inhibitory control, heart rate variability, and countermovement jump

BACKGROUND

The effect of MF induced by exposure time to social media smartphone apps on inhibitory control, heart rate variability (HRV), and high-intensity physical effort following a resistance exercise session might indicate whether strength and conditioning professionals should suggest avoiding smartphone usage before a resistance exercise session.

AIM

The objective of this study was to analyze the effect of mental fatigue on inhibitory control, HRV, and countermovement jump (CMJ) in trained adults after resistance exercise.

METHODS

A total of 16 trained males (21.4 ± 3.3 years) volunteered in this study. The participants performed resistance exercises with and without mental fatigue. The Stroop Task, countermovement jump, and heart rate variability were evaluated before and after the resistance exercise. The participants used smartphones in the mental fatigue condition, whereas the participants watched TV in the control condition.

RESULTS

No condition × time interaction was found for the Stroop accuracy (p = 0.87), CMJ (p = 0.68), SDNN (p = 0.15), or pNN50 (p = 0.15) in the heart rate variability. An interaction was found for Stroop response time (p = 0.01) with a higher response time for the mental fatigue condition (p = 0.01).

CONCLUSIONS

Mental fatigue impaired the inhibitory control performance after a resistance exercise session in trained adults.

"A sprained ankle is the biggest sign of mental fatigue": A qualitative study of the perceptions and experiences of mental fatigue in professional ballet

Mental fatigue is known to influence endurance, skill, and tactical performance in sport. Research investigating the impact of mental fatigue on tasks that combine physical, cognitive, and aesthetic performance such as professional ballet does not exist.

OBJECTIVE

To understand the perceptions and experiences of mental fatigue in professional ballet.

DESIGN

Qualitative, focus groups and semi-structured interviews.

SETTING

The Australian Ballet.

PARTICIPANTS

Thirty-nine professional ballet dancers (53% of the company) and six dance staff members aged 18 years or above (53% female).

MAIN OUTCOME MEASURES

N/a.

RESULTS

The average focus group and interview length was 48 ± 7 min and 41 ± 8 min. Key categories were; (1) Dancers and dance staff perceive that new learning contributes to mental fatigue, (2) Dancers perceive changes to their mood and perception of effort when they are mentally fatigued, and (3) Dancers and dance staff perceive that mental fatigue negatively affects their physical and cognitive performance and, increases their risk of injury.

CONCLUSION

This is the first study where participants associated mental fatigue with injury risk and provides a springboard to measure the impact of mental fatigue on learning, injury, and performance in professional ballet.

Global practitioner assessment and management of mental fatigue and mental recovery in high-performance sport: A need for evidence-based best-practice guidelines

BACKGROUND

Mental fatigue and mental recovery have gained scientific attention in relation to sporting performance, yet best practice assessment and management methods are lacking. A greater understanding of current knowledge and practices in high-performance sport are necessary.

OBJECTIVE

To understand the contemporary knowledge, beliefs, monitoring processes, management strategies, perceived responsibility, sources of evidence, and challenges, when assessing the mental fatigue and mental recovery of athletes in high-performance sport.

METHODS

A mixed-methods survey approach obtained information from 156 multi-disciplinary high-performance sport practitioners. Descriptive outputs were reported and potential differences between key concepts were detected using Wilcoxon-signed rank analysis. Thematic analysis interpreted open-text responses.

RESULTS

Only 11.5% and 5.1% of respondents indicated they were "very" knowledgeable about mental fatigue and mental recovery, respectively. Knowledge (p < 0.001) and confidence in application (p = 0.001) were significantly greater for mental fatigue than mental recovery. Nearly all respondents perceived mental fatigue and mental recovery impacted training and competition performance, with a greater negative impact during competition (p < 0.001). A limited number of respondents reported deliberate assessment (31.1%) or management (51.2%) of mental fatigue and mental recovery. A combination of sources of evidence were used to inform practice, with common challenges to implementation including staff knowledge, athlete-buy in, time-availability, and a lack of evidence. Practitioners reported that assessing and managing mental fatigue and mental recovery was multi-disciplinary in nature.

CONCLUSION

Practitioners reported that mental fatigue and mental recovery did impact performance, yet this was not reflected in the implementation of evidence-based assessment and management practices in high-performance sport.

More than energy cost: multiple benefits of the long Achilles tendon in human walking and running

Elastic strain energy that is stored and released from long, distal tendons such as the Achilles during locomotion allows for muscle power amplification as well as for reduction of the locomotor energy cost: as distal tendons perform mechanical work during recoil, plantar flexor muscle fibres can work over smaller length ranges, at slower shortening speeds, and at lower activation levels. Scant evidence exists that long distal tendons evolved in humans (or were retained from our more distant Hominoidea ancestors) primarily to allow high muscle-tendon power outputs, and indeed we remain relatively powerless compared to many other species. Instead, the majority of evidence suggests that such tendons evolved to reduce total locomotor energy cost. However, numerous additional, often unrecognised, advantages of long tendons may speculatively be of greater evolutionary advantage, including the reduced limb inertia afforded by shorter and lighter muscles (reducing proximal muscle force requirement), reduced energy dissipation during the foot-ground collisions, capacity to store and reuse the muscle work done to dampen the vibrations triggered by foot-ground collisions, reduced muscle heat production (and thus core temperature), and attenuation of work-induced muscle damage. Cumulatively, these effects should reduce both neuromotor fatigue and sense of locomotor effort, allowing humans to choose to move at faster speeds for longer. As these benefits are greater at faster locomotor speeds, they are consistent with the hypothesis that running gaits used by our ancestors may have exerted substantial evolutionary pressure on Achilles tendon length. The long Achilles tendon may therefore be a singular adaptation that provided numerous physiological, biomechanical, and psychological benefits and thus influenced behaviour across multiple tasks, both including and additional to locomotion. While energy cost may be a variable of interest in locomotor studies, future research should consider the broader range of factors influencing our movement capacity, including our decision to move over given distances at specific speeds, in order to understand more fully the effects of Achilles tendon function as well as changes in this function in response to physical activity, inactivity, disuse and disease, on movement performance.

Effect of brain endurance training on maximal oxygen uptake, time-to-exhaustion, and inhibitory control in runners

We aimed to analyze the effect of brain endurance training on maximum oxygen consumption (VO2máx ), time-to-exhaustion, and inhibitory control in amateur trained runners. We employed a mixed experimental design, with the group as the between-participant factor and time as the within-participant factor. 45 participants attended 36 training sessions over 12 weeks. The cognitive training group (CT) performed the Stroop word-color task [trials of each type (congruent, incongruent, and neutral) were randomly presented during each training session], the endurance training group (ET) participated in a running training program (intensity was 60%Δ of maximal aerobic velocity and performed on a motor-driven treadmill), and the brain endurance training group (BET) make cognitive and endurance training simultaneously over 12 weeks. The total time of each session (i.e., 20-40 min) was identical in the experimental groups. VO2máx , time-to-exhaustion, and inhibitory control tests were measured before (baseline) and after (post-experiment) the 12-week intervention. A significant effect of interaction (group × time) for VO2máx (p < 0.05) was found. A post-hoc test showed an increase in VO2máx from baseline to post-experiment only for ET (Δ% = 2.98) and BET (Δ% = 3.78) groups (p < 0.05). Also, the analyses showed a significant interaction (group × time) for time-to-exhaustion (p < 0.05), and a post-hoc test revealed an improvement in time-to-exhaustion for ET (Δ% = 8.81) and BET (Δ% = 11.01) (p < 0.05). No group × time interaction was found for accuracy and response time in the inhibitory control task (p > 0.05). The results conclude that BET was not superior to ET for improving VO2máx and time-to-exhaustion. Also, the findings conclude that BET improved inhibitory control similar to CT.

Post-COVID-19 syndrome: Physical capacity, fatigue and quality of life

PURPOSE

Post-Covid-19 syndrome is defined as the persistence of symptoms beyond 3 months after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The most common symptoms include reduced exercise tolerance and capacity, fatigue, neurocognitive problems, muscle pain and dyspnea. The aim of our work was to investigate exercise capacity and markers of subjective wellbeing and their independent relation to post-COVID-19 syndrome.

PATIENTS AND METHODS

We examined a total of 69 patients with post-COVID-19 syndrome (23 male/46 female; age 46±12 years; BMI 28.9±6.6 kg/m2) with fatigue and a score ≥22 in the Fatigue Assessment Scale (FAS). We assessed exercise capacity on a cycle ergometer, a 6-minute walk test, the extent of fatigue (FAS), markers of health-related quality of life (SF-36 questionnaire) and mental health (HADS).

RESULTS

On average the Fatigue Assessment Scale was 35.0±7.4 points. Compared with normative values the VO2max/kg was reduced by 8.6±5.8 ml/min/kg (27.7%), the 6MWT by 71±96 m (11.9%), the health-related quality of life physical component score by 15.0±9.0 points (29.9%) and the mental component score by 10.6±12.8 points (20.6%). Subdivided into mild fatigue (FAS score 22-34) and severe fatigue (FAS score ≥35), patients with severe fatigue showed a significant reduction of the 6-minute walk test by 64±165 m (p<0.01) and the health-related quality of life physical component score by 5.8±17.2 points (p = 0.01). In multiple regression analysis age (β = -0.24, p = 0.02), sex (β = 0.22, p = 0.03), mental (β = -0.51, p<0.01) and physical (β = -0.44, p<0.01) health-related quality of life and by trend the 6-minute walk test (β = -0.22, p = 0.07) were associated with the FAS.

CONCLUSION

Patients with post-COVID-19 syndrome show reduced maximal and submaximal physical performance as well as limitations in quality of life, particularly pronounced in the physical components. These results are essentially influenced by the severity of fatigue and implicating the need for targeted treatments.

Head-to-head opponent mitigates mental fatigue effects during a 20-km time trial in well-trained cyclists

We aimed to analyze the effect of a head-to-head virtual race on 20-km time trial performance in well-trained mentally fatigued cyclists. A total of 24 male professional cyclists participated in the present study, which was conducted in a within-factors design [four experimental conditions × four times (throughout 20-km time trial cycling)]. An avatar representing the participant on the racecourse was visible during the time trials. Then, a second virtual avatar representing the opponent was projected onto the screen in the mental fatigue head-to-head and control head-to-head experimental conditions. Measurements [rating of perceived exertion, heart rate, and eye-tracking measures (i.e., pupil diameter)] were performed every 5-km throughout the 20-km time trial. As a result, impaired total time, power output, and cadence throughout the 20-km cycling time trial were found for mental fatigue compared to mental fatigue head-to-head, control head-to-head, and control conditions (p < 0.05). Also, impaired 20-km time trial performance (total time, power output, and cadence) was found for mental fatigue head-to-head compared to control head-to-head (p < 0.05). Moreover, lower RPE was found for the control and control head-to-head conditions than mental fatigue head-to-head and mental fatigue experimental conditions (p < 0.05). Higher pupil diameter was also found for mental fatigue head-to-head, control head-to-head, and control than the mental fatigue experimental condition (p < 0.05). In summary, the overall performance throughout the 20-km cycling time trial was improved by the presence of a virtual opponent for the mentally fatigued cyclists.

Transforming fatigue assessment: Smartphone-based system with digitized motor skill tests

BACKGROUND

The condition of fatigue is a complex and multifaceted disorder that encompasses physical, mental, and psychological dimensions, all of which contribute to a decreased quality of life. Smartphone-based systems are gaining significant research interest due to their potential to provide noninvasive monitoring and diagnosis of diseases.

OBJECTIVE

This paper studies the feasibility of using smartphones to collect motor skill related data for machine learning based fatigue detection. The authors' main goal is to provide valuable insights into the nature of fatigue and support the development of more effective interventions to manage it.

METHODS

An application for smartphones running on Android OS is developed. Two aim-based reaction tests, an Archimedean spiral test, and a tremor test, were assembled. 41 subjects participated in the study. The resulting dataset consists of 131 trials of fatigue assessment alongside digital signals extracted from the motor skill tests. Six machine learning classifiers were trained on computed features extracted from the collected digital signals.

RESULTS

The collected dataset SmartPhoneFatigue is presented for further research. The real-world utility of this database was shown by creating a methodology to construct a fatigue predictive model. Our approach incorporated 60 distinct features, such as kinematic, angular, aim-based, and tremor-related measures. The machine learning models exhibited a high degree of prediction rate for fatigue state, with an accuracy exceeding 70%, sensitivity surpassing 90%, and an f1-score greater than 80%.

CONCLUSION

The results demonstrate that the proposed smartphone-based system is suitable for motion data acquisition in non-controlled environments and shows promise as a more objective and convenient method for measuring fatigue.

The impact of sprint, middle-distance, and long-distance orienteering races on perceived mental fatigue in national level orienteers

Experiencing mental fatigue (MF) before an orienteering race can lead to a slower completion time. This study aimed to explore the changes in perceived MF, mood and other psychological responses during an orienteering competition. Sixteen national level orienteering athletes (20.8 ± 4.9 years) provided informed consent and completed the online surveys, before and immediately after each race, and 24- and 48-hours post competition (48POST). This study measured MF, physical fatigue, stress, tiredness and motivation using 0-100 Visual Analogue Scale, and the mood was assessed using The Brunel Mood Scale (BRUMS). A moderate to large increase in MF (ES = 0.93 [0.54 to 1.31]), BRUMS fatigue (ES = 0.61 [0.3 to 0.92]), and PF (ES = 1.21 [0.81 to 1.61]) was reported following orienteering races. A small increase in tiredness and BRUMS confusion, and a small decrease in motivation, stress and BRUMS vigour was also reported. There was a delay in recovering from the MF elicited by competition, with a small increase in MF (ES = 0.54 [0.08 to 1.15]) at 48POST compared to the pre-competition value. This study found that orienteers experience MF during competition and have a delayed recovery that can last up to two days after the competition.

Mental fatigue impairs physical performance but not the neural drive to the muscle: a preliminary analysis

Mental fatigue (MF) does not only affect cognitive but also physical performance. This study aimed to explore the effects of MF on muscle endurance, rate of perceived exertion (RPE), and motor units' activity. Ten healthy males participated in a randomised crossover study. The subjects attended two identical experimental sessions separated by 3 days with the only difference of a cognitive task (incongruent Stroop task [ST]) and a control condition (watching a documentary). Perceived MF and motivation were measured for each session at baseline and after each cognitive task. Four contractions at 20% of maximal voluntary contraction (MVIC) were performed at baseline, after each cognitive and after muscle endurance task while measuring motor units by high-density surface electromyography. Muscle endurance until failure at 50% of MVIC was measured after each cognitive task and the RPE was measured right after failure. ST significantly increased MF (p = 0.001) reduced the motivation (p = 0.008) for the subsequent physical task and also impaired physical performance (p = 0.044). However, estimates of common synaptic inputs and motor unit discharge rates as well as RPE were not affected by MF (p > 0.11). In conclusion, MF impairs muscle endurance and motivation for the physical task but not the neural drive to the muscle at any frequency bands. Although it is physiologically possible for mentally fatigued subjects to generate an optimal neuromuscular function, the altered motivation seems to limit physical performance. Preliminarily, our results suggest that the corticospinal pathways are not affected by MF.

Work performance in industry: The impact of mental fatigue and a passive back exoskeleton on work efficiency

Mental fatigue (MF) is likely to occur in the industrial working population. However, the link between MF and industrial work performance has not been investigated, nor how this interacts with a passive lower back exoskeleton used during industrial work. Therefore, to elucidate its potential effect(s), this study investigated the accuracy of work performance and movement duration through a dual task paradigm and compared results between mentally fatigued volunteers and controls, with and without the exoskeleton. No main effects of MF and the exoskeleton were found. However, when mentally fatigued and wearing the exoskeleton, movement duration significantly increased compared to the baseline condition (β_MF:Exo = 0.17, p = .02, ω² = .03), suggesting an important interaction between the exoskeleton and one's psychobiological state. Importantly, presented data indicate a negative effect on production efficiency through increased performance time. Further research into the cognitive aspects of industrial work performance and human-exoskeleton interaction is therefore warranted.

A Quantitative Investigation of Mental Fatigue Elicited during Motor Imagery Practice: Selective Effects on Maximal Force Performance and Imagery Ability

In the present study, we examined the development of mental fatigue during the kinesthetic motor imagery (MI) of isometric force contractions performed with the dominant upper limb. Participants (n = 24) underwent four blocks of 20 MI trials of isometric contractions at 20% of the maximal voluntary contraction threshold (20% MVC_MI) and 20 MI trials of maximal isometric contractions (100% MVC_MI). Mental fatigue was assessed after each block using a visual analogue scale (VAS). We assessed maximal isometric force before, during and after MI sessions. We also assessed MI ability from self-report ratings and skin conductance recordings. Results showed a logarithmic pattern of increase in mental fatigue over the course of MI, which was superior during 100% MVC_MI. Unexpectedly, maximal force improved during 100% MVC_MI between the 1st and 2nd evaluations but remained unchanged during 20% MVC_MI. MI ease and vividness improved during 100% MVC_MI, with a positive association between phasic skin conductance and VAS mental fatigue scores. Conversely, subjective measures revealed decreased MI ability during 20% MVC_MI. Mental fatigue did not hamper the priming effects of MI on maximal force performance, nor MI's ability for tasks involving high physical demands. By contrast, mental fatigue impaired MI vividness and elicited boredom effects in the case of motor tasks with low physical demands.

Monitoring cognitive function in the fatigued warfighter: A rapid review of cognitive biomarkers

OBJECTIVES

Decreases in cognitive function impair occupational performance, reduce occupational safety, and increase musculoskeletal injury risk. The aim of this paper was to identify measures that may be used to monitor cognitive function in the warfighter.

DESIGN

A rapid review.

METHODS

A rapid search of Academic Search Complete, MEDLINE, PsycINFO, and SPORTSDiscus databases was conducted.

ELIGIBILITY CRITERIA

original peer reviewed research articles, written in English, published between 2002 and 2022, and using human participants with no health issues in military training environments or active service.

RESULTS

Of the 248 articles screened, 58 full-text articles were assessed for eligibility and 29 included in the review. Of these, 16 papers presented data from multi-stressor military training environments, or experimental studies where simulated military tasks were being performed. Thirteen papers focused on an aspect of military work and the implications for cognitive function (i.e., physical load, periods of extended wakefulness or fatigue, and hypoxic conditions). The domains of cognitive function that were assessed (i.e. vigilance, reaction time, working memory, situational awareness, and decision-making) were somewhat consistent among studies.

CONCLUSIONS

Prolonged exposure to high-stress military environments compromises multiple aspects of cognitive function. These findings highlight the need for a suite of biomarkers to monitor cognitive function and assess the ability of military personnel to attend to and process mission-critical information and make appropriate decisions on the battlefield and other high-stress environments. Our findings suggest that a suite of common tests may provide useful information about cognitive function in the warfighter.

Playing videogames or using social media applications on smartphones causes mental fatigue and impairs decision-making performance in amateur boxers

This study aimed to analyze the effect of playing videogames and using social media applications on smartphones on decision-making and countermovement jump (CMJ) performance in amateur boxers. Twenty one boxers were enrolled in the study and were randomly assigned to all three experimental conditions [smartphone (30SMA), videogame (30VID), and control (CON)]. CMJ was measured before and 30-min after each experimental condition. The athletes ran simulated combat recorded for decision-making analysis. The boxers watched coaching videos (CON), used social media applications on smartphones (30SMA), and played video games (30VID) for 30 min just before the combat simulation. Both attack and defense decision-making performance were worse in both 30SMA and 30VID conditions compared to the CON condition (p = 0.001). Regarding CMJ, despite no condition effect (p = 0.96) been obtained, a time effect (p = 0.001) was observed; So, it was found a decrease in CMJ performance after all experimental conditions (p = 0.001), with no difference between them. Using social media applications on smartphones and playing video game impairs decision-making performance in amateur boxers, with no harms for CMJ performance.

Interindividual Variability in Mental Fatigue-Related Impairments in Endurance Performance: A Systematic Review and Multiple Meta-regression

BACKGROUND

The negative effect of mental fatigue (MF) on physical performance has recently been questioned. One reason behind this could lie in the interindividual differences in MF-susceptibility and the individual features influencing them. However, the range of individual differences in mental fatigue-susceptibility is not known, and there is no clear consensus on which individual features could be responsible for these differences.

OBJECTIVE

To give an overview of interindividual differences in the effects of MF on whole-body endurance performance, and individual features influencing this effect.

METHODS

The review was registered on the PROSPERO database (CRD42022293242). PubMed, Web of Science, SPORTDiscus and PsycINFO were searched until the 16th of June 2022 for studies detailing the effect of MF on dynamic maximal whole-body endurance performance. Studies needed to include healthy participants, describe at least one individual feature in participant characteristics, and apply at least one manipulation check. The Cochrane crossover risk of bias tool was used to assess risk of bias. The meta-analysis and regression were conducted in R.

RESULTS

Twenty-eight studies were included, with 23 added to the meta-analysis. Overall risk of bias of the included studies was high, with only three presenting an unclear or low rating. The meta-analysis shows the effect of MF on endurance performance was on average slightly negative (g = - 0.32, [95% CI - 0.46; - 0.18], p < 0.001). The multiple meta-regression showed no significant influences of the included features (i.e. age, sex, body mass index and physical fitness level) on MF-susceptibility.

CONCLUSIONS

The present review confirmed the negative impact of MF on endurance performance. However, no individual features influencing MF-susceptibility were identified. This can partially be explained by the multiple methodological limitations such as underreporting of participant characteristics, lack of standardization across studies, and the restricted inclusion of potentially relevant variables. Future research should include a rigorous description of multiple different individual features (e.g., performance level, diet, etc.) to further elucidate MF mechanisms.

Endogenous and Exogenous Antioxidants in Skeletal Muscle Fatigue Development during Exercise

Muscle fatigue is defined as a decrease in maximal force or power generated in response to contractile activity, and it is a risk factor for the development of musculoskeletal injuries. One of the many stressors imposed on skeletal muscle through exercise is the increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which intensifies as a function of exercise intensity and duration. Exposure to ROS/RNS can affect Na⁺/K⁺-ATPase activity, intramyofibrillar calcium turnover and sensitivity, and actin-myosin kinetics to reduce muscle force production. On the other hand, low ROS/RNS concentrations can likely upregulate an array of cellular adaptative responses related to mitochondrial biogenesis, glucose transport and muscle hypertrophy. Consequently, growing evidence suggests that exogenous antioxidant supplementation might hamper exercise-engendering upregulation in the signaling pathways of mitogen-activated protein kinases (MAPKs), peroxisome-proliferator activated co-activator 1α (PGC-1α), or mammalian target of rapamycin (mTOR). Ultimately, both high (exercise-induced) and low (antioxidant intervention) ROS concentrations can trigger beneficial responses as long as they do not override the threshold range for redox balance. The mechanisms underlying the two faces of ROS/RNS in exercise, as well as the role of antioxidants in muscle fatigue, are presented in detail in this review.

International orienteering experts' consensus on the definition, development, cause, impact and methods to reduce mental fatigue in orienteering: A Delphi study

Orienteering is an outdoor activity wherein participants use a map and compass to locate control points and choose the quickest path to the next control point in a natural environment. Attentional focus, rapid decision-making, and high aerobic fitness may influence orienteering performance. Therefore, this research aimed to seek international orienteering expert consensus regarding the definition, development, causes, influences and methods to reduce mental fatigue (MF) in orienteering based on practical experience. Following ethical approval, a three-round Delphi survey was conducted online with twenty-four orienteering coaches and athletes (or former athletes) from 10 different countries with international orienteering competition experience. The threshold of consensus was ≥ 70% agreement among respondents. The experts agreed that MF exists in daily life and orienteering with a substantial negative effect on their conscious decision-making performance and psychological responses. The experts disagreed that the form of MF that athletes experienced in orienteering training are similar to the competition. However, there was no agreement that MF would impact endurance and high-speed running performance during orienteering. This research refines the definition of MF and summarises the distinctions in what causes MF in orienteering training and competition, implying that MF should be addressed separately.

Probing the Promises of Noninvasive Transcranial Electrical Stimulation for Boosting Mental Performance in Sports

While the importance of physical abilities is noncontested to perform in elite sport, more focus has recently been turned toward cognitive processes involved in sport performance. Practicing any sport requires a high demand of cognitive functioning including, but not limited to, decision-making, processing speed, working memory, perceptual processing, motor functioning, and attention. Noninvasive transcranial electrical stimulation (tES) has recently attracted considerable scientific interest due to its ability to modulate brain functioning. Neuromodulation apparently improves cognitive functions engaged in sports performance. This opinion manuscript aimed to reveal that tES is likely an adjunct ergogenic resource for improving cognitive processes, counteracting mental fatigue, and managing anxiety in elite athletes. Nevertheless, the first evidence is insufficient to guarantee its real effectiveness and benefits. All tES techniques could be add-ons to make performance-related cognitive functions more efficient and obtain better results. Modulating inhibitory control through tES over the frontal cortex might largely contribute to the improvement of mental performance. Nevertheless, studies in elite athletes are required to assess the long-term effects of tES application as an ergogenic aid in conjunction with other training methods (e.g., neurofeedback, mental imagery) where cognitive abilities are trainable.

Effects of molecular hydrogen supplementation on fatigue and aerobic capacity in healthy adults: A systematic review and meta-analysis

Background

Fatigue is oftentimes induced by high-intensity exercise potentially via the exceeded amount of reactive oxygen species, leading to diminished functions (e.g., aerobic capacity) and increased risk of injuries. Studies indicate that molecular hydrogen (H₂), with antioxidant and anti-inflammatory properties, may be a promising strategy to alleviate fatigue and improve aerobic capacity. However, such effects have not been comprehensively characterized.

Objective

To systematically assess the effects of in taking H₂ on fatigue and aerobic capacity in healthy adults.

Methods

The search was conducted in August 2022 in five databases. Studies with randomized controlled or crossover designs that investigated the rating of perceived exertion (RPE), maximal oxygen uptake (VO_2max), peak oxygen uptake (VO_2peak), and endurance performance were selected. The data (mean ± standard deviation and sample size) were extracted from the included studies and were converted into the standardized mean difference (SMD). Random-effects meta-analyses were performed. Subgroup analysis was used to analyze potential sources of heterogeneity due to intervention period, training status, and type of exercise.

Results

Seventeen publications (19 studies) consisting of 402 participants were included. The pooled effect sizes of H₂ on RPE (SMD_pooled = -0.38, 95%CI -0.65 to -0.11, p = 0.006, I ² = 33.6%, p = 0.149) and blood lactate (SMD_pooled = -0.42, 95% CI -0.72 to -0.12, p = 0.006, I ² = 35.6%, p = 0.114) were small yet significant with low heterogeneity. The pooled effect sizes of H₂ on VO_2max and VO_2peak (SMD_pooled = 0.09, 95% CI -0.10 to 0.29, p = 0.333, I ² = 0%, p = 0.998) and endurance performance (SMD_pooled = 0.01, 95% CI -0.23 to 0.25, p = 0.946, I ² = 0%, p > 0.999) were not significant and trivial without heterogeneity. Subgroup analysis revealed that the effects of H₂ on fatigue were impacted significantly by the training status (i.e., untrained and trained), period of H₂ implementation, and exercise types (i.e., continuous and intermittent exercises).

Conclusions

This meta-analysis provides moderate evidence that H₂ supplementation alleviates fatigue but does not enhance aerobic capacity in healthy adults.

Systematic review registration

www.crd.york.ac.uk/PROSPERO/, identifier: CRD42022351559.

Fatigue and Human Performance: An Updated Framework

Fatigue has been defined differently in the literature depending on the field of research. The inconsistent use of the term fatigue complicated scientific communication, thereby limiting progress towards a more in-depth understanding of the phenomenon. Therefore, Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) proposed a fatigue framework that distinguishes between trait fatigue (i.e., fatigue experienced by an individual over a longer period of time) and motor or cognitive task-induced state fatigue (i.e., self-reported disabling symptom derived from the two interdependent attributes performance fatigability and perceived fatigability). Thereby, performance fatigability describes a decrease in an objective performance measure, while perceived fatigability refers to the sensations that regulate the integrity of the performer. Although this framework served as a good starting point to unravel the psychophysiology of fatigue, several important aspects were not included and the interdependence of the mechanisms driving performance fatigability and perceived fatigability were not comprehensively discussed. Therefore, the present narrative review aimed to (1) update the fatigue framework suggested by Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) pertaining the taxonomy (i.e., cognitive performance fatigue and perceived cognitive fatigue were added) and important determinants that were not considered previously (e.g., effort perception, affective valence, self-regulation), (2) discuss the mechanisms underlying performance fatigue and perceived fatigue in response to motor and cognitive tasks as well as their interdependence, and (3) provide recommendations for future research on these interactions. We propose to define motor or cognitive task-induced state fatigue as a psychophysiological condition characterized by a decrease in motor or cognitive performance (i.e., motor or cognitive performance fatigue, respectively) and/or an increased perception of fatigue (i.e., perceived motor or cognitive fatigue). These dimensions are interdependent, hinge on different determinants, and depend on body homeostasis (e.g., wakefulness, core temperature) as well as several modulating factors (e.g., age, sex, diseases, characteristics of the motor or cognitive task). Consequently, there is no single factor primarily determining performance fatigue and perceived fatigue in response to motor or cognitive tasks. Instead, the relative weight of each determinant and their interaction are modulated by several factors.

The effects of mental fatigue on sport-specific motor performance among team sport athletes: A systematic scoping review

Background

The psychobiological state known as mental fatigue (MF) is by engaging in mentally taxing activities for an extended period, which is typically found in team sports, of the high cognitive demand and unpredictable environment. It increases the perception of effort and influences executive functions, impairing sport-specific performance in athletes. However, the consequences of MF on sport-specific motor performance (SSMP) among athletes in team sports remain unclear.

Objective

This scoping review seeks to find and map research publications that investigate the effect of MF on SSMP in team sports.

Methods

Web of Science, Scopus, and PubMed were searched as the main databases, and CENTRAL, Psychology, and Behavioral Sciences Collection, SPORTDicus obtained from EBSCOhost, as well as gray literature was searched for relevant literature and Google Scholar. Cognitive tasks before the SSMP exam are the focus of the selected literature on mental exhaustion. Only experiments testing mental and non-mental exhaustion were chosen.

Results

Twelve studies fulfill the requirement of selection criteria. SSMP in team sports, including soccer, basketball, cricket, and Australian football mainly is examined as physical and technical performance. More specifically, MF significantly influenced physical performance measured as intermittent endurance and total distance (P < 0.05), while data was inclusive when assess in an ecological setting (e.g., small-sided game) (P > 0.05). Technical performance was mainly measured as ball loss, errors in passing and shooting, interception, and successful tackle and showed a dramatic impairment (P < 0.05). The decline of physical activity is relevant with higher level PRE, while decreased technical performance is related to impaired attention resources shown as visual perceptual.

Conclusion

MF adversely influences SSMP in team sports. The most relevant theory for future study to examine the impacts of MF on team-sport athletes could be the psychological model of exercise and its potential extension on attention resources, rather than the traditional "catastrophe" theory.

Psychological Wellbeing and Perceived Fatigue in Competitive Athletes after SARS-CoV-2 Infection 2 Years after Pandemic Start: Practical Indications

The COVID-19 pandemic deeply affected sports and athletes, influencing performance and psychological wellbeing. In order to provide useful guidelines for coaches, a web-based survey was conducted. Three web-based questionnaires were administered during the last phase of the Omicron wave to a total of 204 Italian athletes (age 24.96 ± 9.82): an informative questionnaire to collect sociodemographic data and infection symptoms information, the Fatigue Severity Scale (FSS) and the General Health Questionnaire-12 (GHQ-12). No differences between infection sequels of different variant typologies were found over the long term after the infection. The most frequently declared symptoms included cough (50%), muscular skeletal impairments (48%) fatigue (43%) and fever (43%). Results showed that female athletes have a higher risk of developing post-COVID-19 symptoms, GHQ-12 worse results (p = 0.005) and greater fatigue (p = 0.0002) than males. No significant difference in infection incidence between high- and low-level athletes was found. Endurance athletes showed greater perceived fatigue than anaerobic sports athletes (p = 0.045). Conclusions: These results suggested the need for specific approaches and continuous updating to differentiate training programs for different athletes during the return to play. Medical controls and daily monitoring of athletes of all levels after the infection could be advisable.

Effects of Mental Fatigue on Strength Endurance: A Systematic Review and Meta-Analysis

The purpose of the present systematic review and meta-analysis was to explore the effects of mental fatigue on upper and lower body strength endurance. Searches for studies were performed in the PubMed/MEDLINE and Web of Science databases. We included studies that compared the effects of a demanding cognitive task (set to induce mental fatigue) with a control condition on strength endurance in dynamic resistance exercise (i.e., expressed as the number of performed repetitions at a given load). The data reported in the included studies were pooled in a random-effects meta-analysis of standardized mean differences. Seven studies were included in the review. We found that mental fatigue significantly reduced the number of performed repetitions for upper body exercises (standardized mean difference: -0.41; 95% confidence interval [-0.70, -0.12]; p = .006; I2 = 0%). Mental fatigue also significantly reduced the number of performed repetitions in the analysis for lower body exercises (standardized mean difference: -0.39; 95% confidence interval [-0.75, -0.04]; p = .03; I2 = 0%). Our results showed that performing a demanding cognitive task-which induces mental fatigue-impairs strength endurance performance. Collectively, our findings suggest that exposure to cognitive tasks that may induce mental fatigue should be minimized before strength endurance-based resistance exercise sessions.

Assessment of Fatigue and Recovery in Sport: Narrative Review

Fatigue is a phenomenon associated with decreases in both physical and cognitive performances and increases in injury occurrence. Competitive athletes are required to complete demanding training programs with high workloads to elicit the physiological and musculoskeletal adaptations plus skill acquisition necessary for performance. High workloads, especially sudden rapid increases in training loads, are associated with the occurrence of fatigue. At present, there is limited evidence elucidating the underlying mechanisms associating the fatigue generated by higher workloads and with an increase in injury risk. The multidimensional nature and manifestation of fatigue have led to differing definitions and dichotomies of the term. Consequently, a plethora of physiological, biochemical, psychological and performance markers have been proposed to measure fatigue and recovery. Those include self-reported scales, countermovement jump performance, heart rate variability, and saliva and serum biomarker analyses. The purpose of this review is to provide an overview of fatigue and recovery plus methods of assessments.

Relations among perceived stress, fatigue, and sleepiness, and their effects on the ambulatory arterial stiffness index in medical staff: A cross-sectional study

Objective

To explore the relations among perceived stress, fatigue, sleepiness, and the pathway of their effects on the ambulatory arterial stiffness index (AASI) among medical staff.

Methods

This cross-sectional study was conducted at a tertiary hospital in Wuhan, China. Perceived stress, fatigue, and sleepiness were measured using the perceived stress scale (PSS), Fatigue assessment scale (FAS), and Epworth Sleepiness Scale (ESS), respectively. AASI was obtained from 24-h ambulatory blood pressure monitoring. Path analysis was used to clarify the relations among the PSS, FAS, and ESS scores, and their relations to AASI values.

Results

A total of 153 participants were included herein. The PSS and FAS correlated with the ESS (r = 0.424, p < 0.001), and the PSS correlated with the FAS (r = 0.614, p < 0.001). In addition, the ESS correlated with the AASI (r = 0.225, p = 0.005). According to the path analysis results, the PSS and FAS had no direct effect on the AASI, but did have an indirect effect on this index (β = 0.059, 95% confidence interval [CI] = 0.017-0.128, p = 0.005; β = 0.059, 95%CI = 0.016-0.135, p = 0.006, respectively) by influencing the ESS (β = 0.263, β = 0.262, p = 0.004).

Conclusion

Sleepiness was a mediator of the effects of perceived stress and fatigue on AASI.

A plausible link between the time-on-task effect and the sequential task effect

Mental fatigue can be studied by using either the time-on-task protocol or the sequential task protocol. In the time-on-task protocol, participants perform a long and effortful task and a decrease in performance in this task is generally observed over time. In the sequential task protocol, a first effortful or control task is followed by a second effortful task. The performance in the second task is generally worse after the effortful task than after the control task. The principal aim of the present experiment is to examine the relationship between these two decrements in performance while concomitantly using a sequential task protocol and assessing the performance of the first effortful task as a function of time-on-task. We expect a positive correlation between these two decrements in performance. A total of 83 participants performed a 30-min fatiguing mental task (i.e., a modified Stroop task) or a control task followed by a time-to-exhaustion handgrip task. As expected, this protocol combining the time-on-task and sequential task protocols allowed us to observe (1) a decrease in performance over time during the Stroop task, (2) a worst performance in the handgrip task after the Stroop task by comparison to the control task, (3) a positive correlation between these two effects. The decrease in performance during the Stroop task also correlated with the subjective measures of boredom and fatigue, whereas the detrimental effect observed in the handgrip task did not. Our findings suggest that the two fatigue-related phenomena share a common mechanism but are not completely equivalent.

Mental fatigue does not substantially alter neuromuscular function in young, healthy males and females

The neuromuscular mechanisms leading to impaired motor performance after mental fatigue (MF) are not well-understood and little is known of sex-specific differences in the neuromuscular response to MF. The purpose of this study was to investigate sex-related differences in the impact of MF on neuromuscular function. Thirty young, healthy adults (15F, 15M) performed the Psychomotor Vigilance Task (PVT) to induce MF and watched the Earth documentary (control) for 30 min in a random and counterbalanced order. Before and after each task, measurements of neuromuscular function during submaximal dorsiflexion contractions were obtained. At the end of the PVT, females and males had a slower reaction time (p<0.001, η²_p=0.41) and reported higher fatigue (p<0.001, η²_p=0.50), suggesting the PVT induced MF. After the PVT, females and males demonstrated a decline in force during 10% maximum voluntary contractions (MVC) (p=0.006, η²_p=0.24), slower motor unit firing rate during 20% MVC (p=0.04, η²_p=0.15) and a longer cortical silent period (p=0.01, η²_p=0.22). However, similar changes were observed in the control condition suggesting MF is unlikely to substantially alter neuromuscular function during submaximal isometric contractions in young, healthy adults. Results also suggest neuromuscular function after a MF task is similar between young, healthy females and males. Further research is required to investigate populations with higher fatigue, such as multiple sclerosis or chronic fatigue syndrome.

Nature exposure might be the intervention to improve the self-regulation and skilled performance in mentally fatigue athletes: A narrative review and conceptual framework

Background

Due to causing inability of self-regulation (ego depletion) and executive functions such as directed attention and visual searching for relevant information (e.g., the ball location and the position of teammates), mental fatigue impairs skilled performance in various sports. On the other hand, natural scenes could improve directed attention, which may considerably benefit visual searching ability and self-regulation. However, nature exposure as a potential intervention to improve skilled performance among mentally fatigued athletes has not been discussed thoroughly.

Purpose

To propose the potential intervention for the impairment of skilled performance among mentally fatigued athletes and generate a framework for future studies.

Methods

A narrative review was applied to search broadly across disciplines, retrieving literature from several databases (PubMed, Web of Science, Scopus, and EBSCOhost).

Results

Thirty-three works of literature including 39 experiments (mental fatigue 15; ego depletion 5; and nature exposure 19) were obtained. Finally, a conceptual framework was built regarding the effect of nature exposure intervention on skilled performance in athletes for future studies.

Conclusion

Three theories (the psychobiological model of exercise performance, the strength model of self-regulation, and attention restoration theory) could be potentially integrated to be a conceptual framework and explain the mechanism of preventing prior mental exertion (e.g., mental fatigue and ego depletion). Future studies could examine more on the duration of the intervention.

Brain Stimulation Over the Motion-Sensitive Midtemporal Area Reduces Deleterious Effects of Mental Fatigue on Perceptual-Cognitive Skills in Basketball Players

The objective of this study was to analyze the effect of anodal transcranial direct current stimulation (a-tDCS) over the motion-sensitive midtemporal area on perceptual-cognitive skills (visuomotor and basketball decision-making skills) in mentally fatigued basketball players. A total of 20 male basketball players were recruited. This was a randomized, double-blinded, and counterbalanced crossover study with two experimental conditions: a-tDCS and Sham. The participants completed the basketball decision-making task and visuomotor skill after performing a 60-min sport-based videogame task with anodal (i.e., a-tDCS) or placebo (Sham) stimulation over the motion-sensitive middle temporal area. Worse response time was observed in visuomotor skill for Sham than a-tDCS postexperiment (p < .05). There was no main condition effect for accuracy of visuomotor skill (p > .05). There was more impairment in accuracy and response time in basketball decision-making skills for the Sham condition than a-tDCS (p < .05). Notably, a-tDCS over the motion-sensitive middle temporal area removed the negative effects of mental fatigue on perceptual-cognitive skills.

Do Cognitive, Physical, and Combined Tasks Induce Similar Levels of Mental Fatigue? Testing the Effects of Different Moderating Variables

Experts have highlighted the importance of coaches knowing the level of mental fatigue (MF) induced by different tasks. This study aimed to compare the mentally fatiguing nature of cognitive, physical, and combined tasks and, additionally, assess the effect of different moderating variables on MF. Twenty-three physically active (16 males: Mage = 24 years; seven females: Mage = 22.57 years) participants performed three experimental sessions: (a) physically fatiguing: 30 min of cycloergometer work (at 65%-75% of maximum heart rate), (b) mentally fatiguing: 30 min of an incongruent Stroop task, and (c) mixed fatiguing: 30 min of combining the physically and mentally fatiguing protocols. Subjective MF (visual analog scale), reaction time (psychomotor vigilance task), and cognitive performance (Stroop) were measured throughout the different protocols. Results showed significant increments in subjective MF after all tasks, with the mental and mixed protocols showing significantly higher increases. Only the mentally fatiguing protocol caused significant impairments in reaction time. No significant effects of sex, years of experience, or degree of mental toughness were observed. These results suggest that the use of all these tasks, and especially the mentally fatiguing exercises, should be avoided immediately prior to competitions due to the negative consequences of MF on performance. Moreover, this effect seems to be independent of the sex, years of experience, or mental toughness of athletes.

Non-invasive brain stimulation over the orbital prefrontal cortex maintains endurance performance in mentally fatigued swimmers

BACKGROUND

Using anodal transcranial direct current stimulation (a-tDCS) on frontal brain areas might be a promising strategy to mitigates mental fatigue and maintain endurance performance swimmers.

OBJECTIVE

The objective was to analyze the effect of a-tDCS over the orbital prefrontal cortex (oPFC) on endurance performance of mentally fatigued female amateur swimmer.

METHODS

Nineteen female amateur swimmers participated in this study. In two experimental visits, the swimmers completed the 3-min all-out tethered swimming after performing a 30-min Stroop test with a-tDCS or placebo (Sham) stimulation over the left-oPFC. The brain stimulation conditions (i.e., a-tDCS and Sham) were performed in a double-blinded and counterbalanced order.

RESULTS

It was found lower critical force, mean force, force minimum, fatigue index, and aerobic impulse for Sham than a-tDCS (p < 0.05). There was no main effect of condition for peak force (p >  0.05).

CONCLUSION

We concluded that a-tDCS applied over the left-oPFC in female amateur swimmers mentally fatigued maintained endurance performance. From a practical point of view, the use of a-tDCS should be considered to counteract harmful cognitive effects and maintain endurance performance during competitive race events.

How to Tackle Mental Fatigue: A Systematic Review of Potential Countermeasures and Their Underlying Mechanisms

INTRODUCTION

Mental fatigue (MF) is a psychobiological state that impairs cognitive as well as physical performance in different settings. Recently, numerous studies have sought ways to counteract these negative effects of MF. An overview of the explored countermeasures for MF is, however, lacking.

OBJECTIVES

The objective of this review is to provide an overview of the different MF countermeasures currently explored in literature. Countermeasures were classified by the timing of application (before, during or after the moment of MF) and type of intervention (behavioural, physiological and psychological).

METHODS

The databases of PubMed (MEDLINE), Web of Science and PsycINFO were searched until March 7, 2022. Studies were eligible when MF was induced using a task with a duration of at least 30 min, when they assessed MF markers in at least two out of the three areas wherein MF markers have been defined (i.e., behavioural, subjective and/or [neuro]physiological) and used a placebo or control group for the countermeasure.

RESULTS

A total of 33 studies investigated one or more countermeasures against MF. Of these, eight studies assessed a behavioural countermeasure, 22 a physiological one, one a psychological countermeasure and two a combination of a behavioural and psychological countermeasure. The general finding was that a vast majority of the countermeasures induced a positive effect on behavioural (e.g., task or sport performance) and/or subjective MF markers (e.g., visual analogue scale for MF or alertness). No definitive conclusion could be drawn regarding the effect of the employed countermeasures on (neuro)physiological markers of MF as only 19 of the included studies investigated these measures, and within these a large heterogeneity in the evaluated (neuro)physiological markers was present.

DISCUSSION

Within the physiological countermeasures it seems that the use of odours during a MF task or caffeine before the MF task are the most promising interventions in combating MF. Promising behavioural (e.g., listening to music) and psychological (e.g., extrinsic motivation) countermeasures of MF have also been reported. The most assumed mechanism through which these countermeasures operate is the dopaminergic system. However, this mechanism remains speculative as (neuro)physiological markers of MF have been scarcely evaluated to date.

CONCLUSION

The present systematic review reveals that a wide range of countermeasures have been found to successfully counteract MF on a subjective, (neuro)physiological and/or behavioural level. Of these, caffeine, odours, music and extrinsic motivation are the most evidenced for countering MF. To provide in-detail practical guidelines for the real-life application of MF countermeasures, more research must be performed into the underlying mechanisms and into the optimal dosage and time of application/intake.

Training Willpower: Reducing Costs and Valuing Effort

The integrative model of effortful control presented in a previous article aimed to specify the neurophysiological bases of mental effort. This model assumes that effort reflects three different inter-related aspects of the same adaptive function. First, a mechanism anchored in the salience network that makes decisions about the effort that should be engaged in the current task in view of costs and benefits associated with the achievement of the task goal. Second, a top-down control signal generated by the mechanism of effort that modulates neuronal activity in brain regions involved in the current task to filter pertinent information. Third, a feeling that emerges in awareness during effortful tasks and reflects the costs associated with goal-directed behavior. The aim of the present article is to complete this model by proposing that the capacity to exert effortful control can be improved through training programs. Two main questions relative to this possible strengthening of willpower are addressed in this paper. The first question concerns the existence of empirical evidence that supports gains in effortful control capacity through training. We conducted a review of 63 meta-analyses that shows training programs are effective in improving performance in effortful tasks tapping executive functions and/or self-control with a small to large effect size. Moreover, physical and mindfulness exercises could be two promising training methods that would deserve to be included in training programs aiming to strengthen willpower. The second question concerns the neural mechanisms that could explain these gains in effortful control capacity. Two plausible brain mechanisms are proposed: (1) a decrease in effort costs combined with a greater efficiency of brain regions involved in the task and (2) an increase in the value of effort through operant conditioning in the context of high effort and high reward. The first mechanism supports the hypothesis of a strengthening of the capacity to exert effortful control whereas the second mechanism supports the hypothesis of an increase in the motivation to exert this control. In the last part of the article, we made several recommendations to improve the effectiveness of interventional studies aiming to train this adaptive function."Keep the faculty of effort alive in you by a little gratuitous exercise every day."James (1918, p. 127).

Transcranial Direct Current Stimulation Enhances Exercise Performance: A Mini Review of the Underlying Mechanisms

Exercise performance (EP) is affected by a combination of factors including physical, physiological, and psychological factors. This includes factors such as peripheral, central, and mental fatigue, external peripheral factors such as pain and temperature, and psychological factors such as motivation and self-confidence. During the last century, numerous studies from different fields of research were carried out to improve EP by modifying these factors. During the last two decades, the focus of research has been mainly moved toward the brain as a dynamic ever-changing organ and the ways changes in this organ may lead to improvements in physical performance. Development of centrally-acting performance modifiers such as level of motivation or sleep deprivation and the emergence of novel non-invasive brain stimulation (NIBS) techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are the key motives behind this move. This article includes three sections. Section Introduction provides an overview of the mechanisms behind the reduction of EP. The main focus of the Effects of tDCS on EP section is to provide a brief description of the effects of tDCS on maximal and submaximal types of exercise and finally, the section Mechanisms Behind the Effects of tDCS on EP provides description of the mechanisms behind the effects of tDCS on EP.

Mental Fatigue Prior to Aerobic Exercise Reduces Exercise Pleasure and Negatively Affects Implicit Attitudes Toward Future Exercise

We investigated the effects of mental fatigue (MF) on affective responses during an aerobic exercise session at moderate intensity. We submitted 12 insufficiently active adults (50% women; M age = 24.9 years, SD = 3.0; M BMI = 24.3 kg/m2; SD = 2.6) to two 30-minute pre-exercise conditions: an MF condition (Stroop Color-Word task) and a control condition (watching a documentary) prior to their performance of 20 minutes of aerobic treadmill exercise at 40–59% of heart rate reserve. The minimum washout interval between conditions was two days. Perceived MF and motivation to perform physical exercise were assessed before and after conditions with a visual analog scale of 100 mm. We assessed participants’ affective and exertion responses with the Feeling Scale, Rating of Perceived Exertion (RPE) and heart rate during every two minutes of physical exercise. Implicit attitudes toward physical exercise were assessed by the Implicit Association Test before the MF and control conditions and after the physical exercise session. The participants in the MF condition reported lower pleasure ( M difference = −1.57, 95% CI = −2.64 to −0.50, d = 0.93, p = .008) and higher exertion (RPE) ( M difference = 1.16, 95% CI = 0.04 to 2.27, d = 0.66, p = .043) compared to those in the control condition. Participants who experienced MF also reported a more negative implicit attitude toward physical exercise than in the control condition ( β = −0.47, 95% CI= −0.73 to −0.21, d = 1.41, p < .001). While these findings should be cross-validated in subsequent research with a larger and more diverse participant sample, there appears to be value in minimizing pre-exercise mental fatigue to avoid negative MF effects on the exercisers’ affective experience.